1. Field of Invention
The present invention relates to measuring gauges and in particular to a gauge for measuring the pitch diameter of a variable speed V-belt pulley.
2. Description of the Prior Art
As shown in FIGS. 1 and 2, a variable speed V-belt pulley typically includes a sheave section 3 having a threaded hub 4 about which an opposing sheave section 5 is threaded to form the track or groove of the pulley. The sheave section 5 is secured in position by a removable key 7 which is slid into a pair of opposing keyways in the hub 4 and the sheave section 5.
In this type of arrangement, the speed ratio of the pulley is adjusted by varying the pitch diameter of the pulley. As indicated by the dimension "PD" in FIG. 2, the pitch diameter is essentially the effective diameter of the pulley which corresponds to the pitch line of the belt where it wraps around the pulley. For example, if the spacing between the opposing sheave sections of the pulley is increased, the pitch diameter will be reduced since the belt will be carried in the groove of the pulley closer to its hub, and conversely, if the spacing between the opposing sheave sections is reduced, the pitch diameter will be increased proportionally.
In order to measure the spacing between the sheave sections in the field, and thus set the pitch diameter of the pulley, it has been the common practice to disassemble the pulley and then reassemble it by rotating the sheave section 5 on the threaded hub 4 a predetermined number of revolutions corresponding to the desired spacing. However, experience has shown this procedure to be time consuming and often difficult to accomplish in the relative confinement of the housings typically used for the heating and air conditioning systems in which this type of pulley is often used.